The present invention relates to the highly branched copolymers of conjugated dienes and monovinylaromatic compounds, which copolymers are particularly useful for forming adhesive compositions.
The preparation of highly branched copolymers, sometimes referred to as "radial" or "star" copolymers is well known in the art. Examples of such known processes are disclosed in U.S. Pat. No. 3,078,254 (Zelinski and Hsieh), U.S. Pat. No. 3,280,084 (Zelinski), U.S. Pat. Nos. 3,281,383 (Zelinski and Hsieh), and 3,639,517 (Kitchen et al), all assigned to Phillips Petroleum Company, the disclosures of which are incorporated herein by reference.
Many of the highly branched polymers that can be produced by the known processes have been found to be particularly useful as the polymeric base for pressure sensitive adhesives. Examples of polymers that are useful in formulating pressure sensitive adhesives include the radial block copolymers that are sold by Phillips Petroleum Company under the trademarks Solprene.RTM.411, 406, and 414.
The compounding of pressure-sensitive adhesives requires the balancing of numerous factors. The mass coat must be soft enough to flow under light pressure to wet the substrate and yet possess sufficient cohesive strength to withstand the stresses of the job it is designed to do. Thus, in addition to providing a material that is tacky an essential property is the holding power.